1. Field of the Invention
This invention relates to combustion chambers for gas turbine engines.
2. Description of the Prior Art
The emphasis today on the design and development of gas turbine engines for jet aircraft is towards pollution control and reduction in engine weight without thrust penalties. Much of this design and development work is centered on the combustor section of the engine which, conventionally, has not provided the clean burning which is now desired. Furthermore, conventional combustors require a considerable axial length to perform the burning process; this increases the overall engine length, which of course results in an increase in engine weight.
Premixing of the fuel with the air is one technique which has been investigated to improve the combustion process. U.S. Pat. No. 2,999,359 to F. R. Murray shows such a technique in FIG. 2. One purpose of all the constructions shown in Murray is to create recirculating counter-rotating zones of combusting fuel and air within the primary combustion zone to improve combustion efficiency. Such recirculation increases the length of time the combusting fuel and air remains in the primary zone of combustion; this is undesirable from a pollution viewpoint since it increases the amounts of oxides of nitrogen produced within the combustion chamber.
Another type of premix combustion chamber is shown in U.S. Pat. No. 2,679,137 to Probert. A mixture of fuel and air is admitted to a primary or pilot combustion zone through a baffle at the forward end of the combustion chamber. Only a portion of the fuel is burned in the primary combustion zone with the remainder of the fuel being burned in a downstream combustion zone upon the entry of additional dilution and combustion air. The reburning of combusting fuel in the downstream zone increases, as in Murray, the length of time that the gases are exposed to combustion temperatures and correspondingly increases the amounts of oxides of nitrogen produced within the combustion chamber. Continuing efforts are being directed to the design of combustion chambers which are capable of fully combusting fuel with a limited axial length while minimizing the recirculation of combusting gas through high temperature zones.